Electronic devices such as radio telephones, two-way radios, and other communication devices, often have an externally accessible connector for interfacing with compatible accessories. Generally, an accessory is designed to operate at a voltage level that is compatible with the voltage level of the electronic device. However, as electronic devices are being designed to operate at lower voltage levels to reduce power consumption requirements or for other purposes, it is desirable to have electronic devices that can interface with accessories designed to operate at different voltage levels. Such flexibility would allow for protection of investments in accessory inventories which may benefit customers and manufacturers alike.
In one solution to the above described problem, a bi-directional voltage translator is provided at the external interface of the electronic device. A prior art application of such a bidirectional voltage translator is described in U.S. Pat. No. 5,680,063 issue to Ludwig et al., on Oct. 21, 1997, for a BI-DIRECTIONAL VOLTAGE TRANSLATOR, the entire contents of which are hereby incorporated by reference. Here, Ludwig describes a switch circuit in which a field effect transistor (FET) device is used to provide a switch circuit for low power applications, i.e., three volts (3V) to five volts (5V) voltage translation. For particular circuit implementations, Ludwig postulated that certain devices were unsuitable for low power application. As an example, at column 7, lines 36-39, Ludwig states that "in low power applications, such as 3V to 5V voltage translation, it is envisioned that the use of BJTs rather than MOSFETs may retard or altogether prevent turn-on of [the] switch circuit."
Ludwig's circuit implementation has been found to be unsuitable for certain low voltage applications, particularly as electronic devices transition from 5 volts to 3 volts to 1.8 volts or lower. Other prior art solutions that use control lines to direct signal flow and voltage translation tend to be more complex. Accordingly, the need exists for a bidirectional voltage translator that is suitable for such low voltage applications, but that avoids the complexity involved with additional control lines.